slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Catherine Trask 2008 PowerPoint Presentation
Download Presentation
Catherine Trask 2008

Loading in 2 Seconds...

play fullscreen
1 / 41

Catherine Trask 2008 - PowerPoint PPT Presentation


  • 85 Views
  • Uploaded on

Balancing Efficiencies & Tradeoffs: Evaluating EMG Exposure Assessment for Low Back Injury Risk Factors in Heavy Industry. Catherine Trask 2008. ‘Solving’ Back Injury. Back injury is a prevalent and expensive problem, particularly in heavy industry. Thesis Objectives.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Catherine Trask 2008' - marika


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Balancing Efficiencies & Tradeoffs:Evaluating EMG Exposure Assessment for Low Back Injury Risk Factors in Heavy Industry

Catherine Trask 2008

solving back injury
‘Solving’ Back Injury
  • Back injury is a prevalent and expensive problem, particularly in heavy industry
thesis objectives
Thesis Objectives
  • How should exposure be measured?
  • For what duration?
  • Who should be measured?
  • How many times should they be measured?
thesis chapters
Thesis Chapters
  • How should exposure be measured?
  • For what duration?
  • Who should be measured?
  • How many times should they be measured?
  • Chapters 4 and 5
  • Chapter 6
  • Chapter 7
  • Chapter 7
thesis chapters1
Thesis Chapters
  • Introduction to exposure assessment
  • Introduction to methods
  • How should exposure be measured?
  • For what duration?
  • Who should be measured?
  • How many times should they be measured?
  • Chapters 1
  • Chapter 2 and 3
  • Chapters 4 and 5
  • Chapter 6
  • Chapter 7
  • Chapter 7
available exposure assessment methods

Direct Measure

using electronic devices

Observation

by trained experts

Self-report

by the workers

Available Exposure Assessment Methods
continuum of methods

Direct Measure

Observation

Self-report

Continuum of Methods

Wider scope – ‘big picture’

Subjective

Inexpensive

More people

Longer time

High-resolution – lots of detail

Objective

Expensive

Few people

Short time

worker recruitment
Worker Recruitment
  • Contacted workers in heavy industry with accepted back injury claims
  • Contacted employer to gain access to the worksite
  • Recruited co-workers at each worksite
  • 126 individuals
  • Repeated measures
  • 223 measurement days
the measurement day

Direct Measure

by electronic devices

Observation

by trained experts

Self-report

by the workers

The Measurement Day
  • Measured all methods concurrently
  • Full shift
risk factors for back injury self report

Self-report

Back

Injury

Risk Factors for Back Injury:Self-Report
  • Asked for the amount of time in each activity
  • Used pictographs for most questions
  • Working Postures

Manual Materials Handling

risk factors for back injury observation

Observation

Back

Injury

Risk Factors for Back Injury:Observation
  • ‘Snapshots’ of 15 variables at 1 minute intervals
  • Full-shift, excluding breaks
  • Working Postures

Manual Materials Handling

risk factors for back injury direct measurement

Whole body vibration

Seat pad accelerometer

Inclinometer

Back muscle activity

EMG

Mean

90th %

Cumulative

RCM

Back

Injury

Risk Factors for Back Injury:Direct Measurement
  • Working Postures

Manual Materials Handling

slide15

Chapter 4: Measuring low back injury risk factors in challenging work environments: an evaluation of cost and feasibility

A version of this chapter has been published. Trask, C., Teschke, K., Village, J., Chow, Y., Johnson, P., Luong, N., and Koehoorn, M. (2007). Evaluating methods to measure low back injury risk factors in challenging work environments. American Journal of Industrial Medicine 50(9):687-96.

cost and feasibility
Cost and Feasibility
  • Success rate = successful measurement/ attempted measurement
  • Cost ($CDN) per successful measurement
conclusions
Conclusions
  • Inverse relationship between cost and feasibility
  • Industrial environments are demanding on mechanical equipment
    • Cold, dusty, wet, explosive,
    • Rough handling/vibration
  • Consider costs and feasibility when planning field work!
slide20

Chapter 5: Predicting exposure for mean, 90th percentile, and cumulative EMG activity in heavy industry

A version of this chapter has been submitted for publication. Trask, C., Teschke, K., Morrison, J., Village, J., Johnson, P., Koehoorn, M. (2008) Predicting Exposure for Mean, 90th Percentile, and Cumulative EMG Activity in Heavy Industry. Submitted February 2008 to: Applied Ergonomics.

modeling determinants of exposure

Low Back EMG

Observation or self report

Modeling determinants of exposure

%RC = β1(observed variable 1) + β2(observed variable 2) + β3(observed variable 3)…

model performance
Model Performance
  • Observation based model
  • Self-report based model
conclusion
Conclusion

Is this enough to conduct injury research?

  • Chemical exposure studies often predict 30-60%
  • Many studies using self-report and observation have found a relationship with back injury in the past
  • Epidemiology often uses categorical exposure variables, not continuous variables
  • One can predict some of the variability in EMG by asking a few questions or observing a few exposures
  • Tradeoff is in measuring more individuals, more times
slide26

Chapter 6: How long is long enough? Selecting efficient sampling durations for low-back EMG assessment

A version of this chapter has been accepted for publication. Trask, C., Koehoorn, M., Village, J., Johnson, P., Teschke, K. (2008) How long is long enough? Evaluating sampling durations for low-back EMG assessment. Journal of Occupational and Environmental Hygiene. Submission number: JOEH-07-0094.R1.

sampling duration rationale
Sampling Duration Rationale
  • Direct measurements were made for a whole shift
  • Do you really need to measure a whole shift?
  • How much information is lost if you measure a portion of the shift?
selecting sampling durations
Selecting sampling durations
  • Compared 7 different sampling durations of the same work shift:
    • Whole shift (5.5 to 7.5 hours)
    • 4 hours
    • 2 hours
    • 1 hour
    • 10 minute
    • 2 minute
    • 2 shifts
  • Re-sampled post hoc
  • Randomized start time
sampling durations

Whole shift

4 hour

2 hour

1 hour

Sampling durations

Green = right back muscles

Red = left back muscles

conclusion1
Conclusion
  • 8% error for 4-hour and 14% error for 2-hour durations: reasonable estimates
  • 1 hour or less produces very large errors
  • Balance cost with data precision and sample size
    • Shorter duration but more workers measured
slide32

Chapter 7: Optimizing sampling strategies: components of low-back EMG variability in five heavy industries

A version of this chapter has been submitted for publication. Trask, C., Teschke, K., Morrison, J., Koehoorn, M. (2007) Optimizing Sampling Strategies: Components of Low-Back EMG Variability in Five Heavy Industries. Submitted February 2008 to: Occupational and Environmental Medicine. Submission number: OEM/2008/039826

components of variability rationale
Components of Variability Rationale
  • How many individuals?
  • How many repeats?
  • (How) should we group measurements?
  • Grouping schemes make for less attenuation of an exposure-response relationship
  • Attenuation can be estimated based on the exposure data, even when the response is not measured
sample exposure response relationship

Response

Exposure

Sample Exposure-ResponseRelationship

Back injury outcome = intercept + β1(exposure variable 1)

grouping schemes
Grouping Schemes
  • No grouping
  • Job title
  • Company
  • Industry
  • Post hoc ranking of industry/job title groups
conclusion2
Conclusion
  • The post hoc grouping scheme was the most efficient grouping scheme
    • Lowest estimated attenuation
    • Lowest number of measurements required
  • Measurement and recruitment challenges mean one should aim for a larger number of measurements
  • Attenuation isn't everything when selecting a sampling strategy – want to choose sample size to be robust
summary
Summary

There are always tradeoffs in exposure assessment

  • Lots of decisions to make!
  • How you ‘tip the scales’ toward more samples or more precision depends on the purpose of the study and the characteristics of the population
  • Contribution is in the ways of framing these questions and starting to quantify the answers
acknowledgements
Acknowledgements

Participating Workers and Worksites

WorkSafe BC

Michael Smith Foundation for Health Research

CIHR Bridge Fellowship Program

Mieke Koehoorn

Kay Teschke

Jim Morrison

Judy Village

Pete Johnson

Jim Ploger

Yat Chow

Kevin Hong

Nancy Luong

Melissa Knott

James Cooper